Low temperature catalysts for methanol production

ABSTRACT

A catalyst and process useful at low temperatures (below about 160° C.) and preferably in the range 80°-120° C. used in the production of methanol from carbon monoxide and hydrogen is disclosed. The catalyst is used in slurry form and comprises a complex reducing agent derived from the component structure NaH--RONa--M(OAc) 2  where M is selected from the group consisting of Ni, Pd, and Co and R is a lower alkyl group containing 1-6 carbon atoms. This catalyst is preferably used alone but is also effective in combination with a metal carbonyl of a group VI (Mo, Cr, W) metal. The preferred catalyst precursor is Nic (where M=Ni and R=tertiary amyl). Mo(CO) 6  is the preferred metal carbonyl if such component is used. The catalyst is subjected to a conditioning or activating step under temperature and pressure, similar to the parameters given above, to afford the active catalyst.

The U.S. Government has rights in this invention pursuant to ContractNumber DE-AC02-76CH00016, between the U.S. Department of Energy andAssociated Universities Inc.

RELATED APPLICATIONS

This is a division of application Ser. No. 710,879 filed Mar. 12, 1985,and now abandoned, which in turn is a continuation-in-part applicationof application Ser. No. 581,935 filed Feb. 21, 1984, and now abandoned.

BACKGROUND OF THE INVENTION

The present application describes a low temperature catalyst and aprocess for the production of methanol utilizing this catalyst. Thiscatalyst allows low temperature and low pressure use for the preparationof methanol in accordance with the equation

    CO+2H.sub.2 →CH.sub.3 OH

The pressure and temperature parameters employed for the reactiongreatly influence the results and are therefore critical. One advantageof the catalyst is that it is useful at low temperatures, up to about160° C., with temperatures in the range of 80°-120° C. being preferred.Another advantage of the catalyst is that it can be used in slurry form.

The catalyst of the present invention consists of a complex reducingagent derived from the component structure NaH--RONa--M(OAc)₂ where M isselected from the group consisting of Ni, Pd, and Co and R is a loweralkyl group containing 1-6 carbon atoms. The preferred complex reducingagent is Nic, in which M=Ni and R=tertiary amyl. Nic is a known agentthat has been used in the past in hydrogenation reactions to convertalkynes to alkenes [Gallois et al., J. Org. Chem., 45, 1946 (1980)].

The reaction CO+2H₂ ⃡CH₃ OH is favored toward the right for theproduction of methanol by a combination of low temperatures andrelatively high pressures. The present process uses a reactiontemperature of about 160° C. or less, preferably in the range of80°-120° C., which is known in the art as a low temperature reaction.

The reaction system is operated at about 50-1000 psi with 300 psipreferred as a starting pressure. In a continuing reaction of decreasingpressure over a span of about two hours, initial pressure of 300 psi wasutilized and a final pressure of 50 psi was achieved. The reactor is ofthe stirred or agitated type and is flushed with hydrogen prior to useand the catalysts are prepared and charged under an inert blanket, suchas argon.

DETAILED DESCRIPTION OF THE INVENTION

The present invention consists of a new series of low temperature, highactivity catalysts for the synthesis of methanol from carbon monoxideand hydrogen. These catalysts are capable of activating hydrogen forreducing carbonyl bonds, and are thus "hydridic" hydrogenating agents.In one embodiment of the invention, a complex reducing agent of the typeNaH--RONa--M(OAc)₂ where M is selected from the group consisting of Ni,Pd, and Co and R is a lower alkyl group having 1-6 carbon atoms is usedin a slurry reactor. The preferred complex reducing agent is where M=Niand the utilization of Ni(OAc)₂ is in combination with the sodiumalcoholate which is derived from tertiary amyl alcohol. This complexreducing agent is known as Nic.

In the complex reducing agent, when M=Ni and where tertiary amyl alcoholis used, the R in the complex is predominantly tertiary amyl. Thus, thepreferred form of this complex reducing agent which is a precursor tothe active form of the catalyst is theoretically a structured form ofnickel, which contains sodium t-amyl alcoholate residues. This catalystthus uses a Group I metal (Na) with a preferred Group VIII metal (Ni).

In another embodiment of the present invention, the catalyst consistingof the complex reducing agent of the formula NaH--ROH--M(OAc)₂ where Mis selected from the group consisting of Ni, Pd, and Co and R is a loweralkyl group containing 1-6 carbon atoms can be incorporated into asystem where the second component in the system consists of a metalcarbonyl selected from the group VI metals (Cr, Mo, W), with Mo(CO)₆being preferred. This catalyst system operates within the sametemperature and pressure ranges as discussed above to convert CO and H₂to methanol. This system not only contains the catalyst capable ofactivating hydrogen for reducing carbonyl bonds, it also contains asecond catalyst, such as molybdenum carbonyl, capable of activatingcarbon monoxide.

PREPARATION OF THE CATALYST SYSTEM

The complex reducing agent catalyst was prepared from a stirredsuspension of NaH added to dry nickel acetate under an inert atmosphere,such as argon, together with tert-amyl alcohol in tetrahydrofuran and anexcess of tertiary amyl alcohol was added to neutralize any excess NaH.A non-pyrophoric black suspension formed and was charged into a stirredpressure reactor under argon. If this catalyst is to be used togetherwith a metal carbonyl, the metal carbonyl is added to the reactor atthis time in a solvent (usually tetrahydrofuran).

SYNTHESIS OF METHANOL

After addition of the catalyst or the catalyst/metal carbonyl system incatalytic amounts to the pressure reactor, said reactor was flushed withhydrogen and the gas mixture (2H₂ :1CO) was added under a pressure ofabout 300 psi. In the stirred reactor, the pressure decreased to about50 psi and at that point the reactor was recharged twice. In a separaterun in a continuous variation, the gas mix (2H₂ :1CO) was charged at 300psi. Gas consumption at up to 8 psi per minute was observed. In oneexperiment, a yield of 2000% based on stoichiometric conversion of thecomplex reducing agent was achieved, with 96% selectivity for methanoland about 4% methyl formate being produced. The reaction rate was about10⁻² turnovers per second (turnovers are here defined as molecules ofmethanol per molecule of catalyst per second).

It is believed that the success of the present catalyst can be explainedby the proposition that the metal catalyzed reactions of synthesis gas(syngas) proceed via chemisorbed carbon monoxide reacting with hydrogento yield an oxygen coordinated species as shown in the followingreaction sequence. ##STR1##

This oxymethylene intermediate can be hydrogenated to methane or canundergo chain growth by reaction with similar species. Hydrogenation mayalso occur across the C═O bond, cleaving the M--O bond and this accountsfor the presence of oxygenated products.

Utilization of the present catalyst gave unusual yields of greater than80% conversion to methanol in a one pass process. When thecatalyst/metal carbonyl system was employed, the yields were between30-35% conversion of methanol in a one pass process. Using the catalystalone or in combination with the metal carbonyl, the process produces aminimum of byproducts and, for example, in a typical run gave 96%methanol based on syngas consumed.

In this specification and claims, a heavy metal salt refers to a GroupVIII heavy metal, especially Ni, Co, and Pd.

The following examples are presented to further describe the invention.

EXAMPLE 1

This example illustrates the preparation, conditioning and use of thecatalyst of the present invention at 100° C. and 750 psi in a batchreactor. To a stirred suspension of sodium hydride (60 mmols), and drynickel acetate (10 mmols) in 25 ml tetrahydrofuran was added dropwise,at 45° C. and under an argon atmosphere, a solution of tertiary amylalcohol (20 mmols) in 5 ml tetrahydrofuran. Stirring was continued for 2hrs. during which time the liquid became black. An additional portion oftertiary amyl alcohol (32 mmol) was then added to neutralize theremaining sodium hydride, and the mixture was allowed to return to roomtemperature. A non-pyrophoric black suspension resulted which was thentransferred under argon to a Parr Model 4561 300 ml stirred pressurereactor to which an additional 70 ml tetrahydrofuran was added. Afterflushing with hydrogen, the reactor was charged with 750 psi of amixture of 33% carbon monoxide in hydrogen and heated to 100° C. Thepressure decreased during the run due to syngas consumption. During thistime the catalyst precursor was "conditioned", that is, converted to theactive catalyst. After 1 hr, the pressure had decreased to 180 psi andthe reactor was cooled. It was then recharged with syngas to 750 psi,heated again to 100° C. and similar gas consumption was observed. Thereactor was cooled and a sample was withdrawn and analyzed. The totalgas charge was 920 mmol with a total pressure drop equivalent to 755mmol gas usage. Gas chromatographic analysis of the liquid showed 185mmol methanol was produced. No methane or carbon dioxide was found inthe gas phase. This amounts to about 74% yield overall based on consumedsyngas, with much of the other consumption associated with conditioning.

EXAMPLE 2

This example illustrates the importance of base to the catalyst systemreaction. The precursor described in Example 1 was loaded into thereactor, charged with 750 psi syngas and brought to 100° C. After about500 psi syngas had been consumed, the reactor was drained of 70 ml ofits liquid contents, leaving the solid plus about 30 ml of liquid. Thesame volume of THF (70 ml) was added and the reactor was recharged with750 psi 33% carbon monoxide with hydrogen. After 31/2 hours at 100° C.,the pressure had decreased to 515 psi. To this system the reactionproduct of 1.2 g sodium hydride and 5 ml tertiary amyl alcohol was addedand the reactor was recharged to 750 psi of the syngas mixture. After2.85 hours the pressure was down to 160 psi. The total gas charge was880 mmol with a total pressure drop equivalent to 560 mmol gas usage.Gas chromatography showed 215 mmol of methanol was produced, includingsome of the methanol produced in the first charging. No methane orcarbon dioxide was found in the gas phase.

EXAMPLE 3

This example illustrates lower temperatures as in Example 1 arepreferred. The catalyst precursor preparation and loading described inExample 1 was repeated and the reactor was charged with 750 psi 33%carbon monoxide in hydrogen. After 1.5 hours at 150° C. the pressure wasdown to 310 psi. With continued heating, no further pressure drop wasobserved. The reactor was recharged with 300 psi of the syngas mixture.After 1.2 hours at 100° C. the reaction had not proceeded and the finalpressure was 380 psi. The reactor was cooled and gas and liquid sampleswere withdrawn. The total gas charge was 362 mmol with a pressure dropequivalent to 86 mmol. Gas chromatography showed 20 mmol of methanol wasproduced.

EXAMPLE 4

This example shows this catalyst used at 120° C. The catalyst precursordescribed in Example 1 was subjected to gas feed of 300 psi syngas (2H₂:CO). After 1 hr at 120° C. the pressure had decreased to 180 psi. Thereactor was recharged three more times with 300 psi and run at 120° C.with similar results. The reaction was cooled and a sample was withdrawnand analyzed. The total gas charge was 740 mmol with a total pressuredrop equivalent to 570 mmol gas usage. Gas chromatography showed 160mmol of methanol was produced.

EXAMPLE 5

This example demonstrates the catalyst used at 80° C. The catalystprecursor described in Example 1 was subjected to 300 psi 33% carbonmonoxide with hydrogen. After 3.4 hours at 80° C. the pressure was downto 120 psi. The reactor was recharged with 300 psi of the syngasmixture. After 1.3 hrs at 80° C. the pressure had dropped to 140 psi.The reactor was cooled and a sample withdrawn and analyzed. The totalgas charge was 360 mmol with a pressure drop equivalent to 255 mmol gasusage. Gas chromatography showed 82 mmol methanol was produced.

EXAMPLE 6

This example demonstrates the catalyst conditioned at 100° C., then usedat 150° C. The catalyst precursor described in Example 1 was subjectedto 300 psi 33% carbon monoxide with hydrogen. After 2.5 hours at 100° C.the pressure was down to 130 psi. The reactor was recharged with 300 psiof the syngas mixture. After 1 hour at 150° C. the pressure was down to210 psi. The reactor was cooled and a sample was withdrawn and analyzed.Gas chromatography showed 54 mmol methanol produced.

EXAMPLE 7

This example shows that the catalyst may be reused. The catalystprecursor described in Example 1 was subjected to gas feed at 300 psi2:1 synthesis gas (2H₂ :CO). After 43 min. at 100° C. the pressure wasdown to 180 psi. The reactor was recharged with 300 psi of the syngasmixture. After 54 min. at 120° C. the pressure was down to 160 psi. Thereactor was recharged two more times under similar conditions. The thirdcharge was at 120° C. for 21 min., allowing the pressure to drop to 180psi. The fourth charge dropped to 120 psi while at 120° C. for 45 min.The reactor was cooled and a sample withdrawn and analyzed.Approximately 5.8 g of syngas was consumed, with analysis indicating 5.0g methanol had been formed, with no significant amounts of other organiccompounds found. The excess gas consumption appears to be due toinorganic side reactions, some of which are related to conditioning.

EXAMPLE 8

This example demonstrates conditioning at 100° C. and use at 80° C. Thecatalyst precursor described in Example 1 was subjected to gas feed of300 psi 33% carbon monoxide with hydrogen. After 90 min. at 100° C. thepressure was down to 170 psi. The reactor was recharged with 300 psi ofthe syngas. After 60 min. at 80° C. the pressure was down to 180 psi.The reactor was recharged again in a similar manner with the sameresults. The reactor was cooled and a sample withdrawn and analyzed. Thetotal gas charge was 550 mmol with a pressure drop equivalent to 306mmol gas usage, affording 2.6 g methanol.

EXAMPLE 9

This example illustrates the preparation, conditioning and use of thecatalyst/metal carbonyl system at 100° C. and 300 psi in a batchreactor.

To a stirred suspension of sodium hydride (60 mmols), and dry nickelacetate (10 mmols) in 25 ml tetrahydrofuran was added dropwise, at 45°C. and under an argon atmosphere, a solution of tertiary amyl alcohol(20 mmols) in 5 ml tetrahydrofuran. Stirring was continued for 2 hrs.during which time the liquid became black. An additional portion oftertiary amyl alcohol (32 mmol) was then added to neutralize theremaining sodium hydride, and the mixture was allowed to return to roomtemperature.

A non-pyrophoric black suspension resulted which was then transferredunder argon to a Parr Model 4561 300 ml stirred pressure reactorcontaining 1.3 g molybdenum hexacarbonyl (5 mmol), to which anadditional 70 ml tetrahydrofuran was added. After flushing withhydrogen, the reactor was charged with 300 psi of a mixture of 33%carbon monoxide in hydrogen and heated to 100° C. The pressure decreasedduring the run due to syngas consumption. During this time the catalystprecursor was "conditioned," that is, converted to the active catalyst.After 2 hr, the pressure had decreased to 50 psi and the reactor wascooled. It was then recharged with syngas to 300 psi, heated again to100° C. and similar gas consumption was observed. After a third chargingand heating cycle, the reactor was cooled and a sample was withdrawn andanalyzed.

The total gas charge was 300 mmol with a total pressure drop equivalentto 270 mmol gas usage. Gas chromatographic analysis of the liquid showed67 mmol methanol was produced. No methane or carbon dioxide was found inthe gas phase. This amounts to about 74% yield overall based on consumedsyngas, with much of the other gas consumption (CO) associated withconditioning.

EXAMPLE 10

The catalyst system described in Example 9 was subjected to gas feed of300 psi 33% carbon monoxide with hydrogen doped with 1670 ppm ofhydrogen sulfide. After 2 hours at 100° C., the system was rechargedwith this same mixture. Analysis after 2 additional hours of reactionshowed 45 mmol methanol which corresponds to a yield of about 33%.

EXAMPLE 11

The catalyst system described in Example 9 with chromium hexacarbonylsubstituted for molybdenum hexacarbonyl gave similar gas consumption asshown in Example 9 at 150° C.

EXAMPLE 12

The catalyst system described in Example 9 with cobalt acetatesubstituted for nickel acetate after 14 hours at 125° C. gave 11%conversion to methanol with a single charge of 300 psi syngas containing33% CO.

We claim:
 1. A catalyst used in the synthesis of methanol from carbonmonoxide and hydrogen which comprises catalytic amounts in slurry formof a complex reducing agent of the type NaH--ROH--M(OAc)₂ wherein M isselected from the group consisting of Ni, Pd, and Co and R is a loweralkyl group containing from 1-6 carbon atoms, combined with a group VImetal carbonyl.
 2. The catalyst of claim 1 wherein the complex reducingagent is derived from NaH--ROH--Ni(OAc)₂.
 3. The catalyst of claim 2wherein R is tertiary amyl.
 4. The catalyst of claim 1 wherein the metalcarbonyl is molybdenum hexacarbonyl.